The present invention relates generally to writing instruments including but not limited to pens, pencils, styluses and markers, and in particular, to a new and useful expandable writing instrument in the form of a mechanical pen, pencil, stylus or marker that has a compact closed position for storage and carry, and an extended open position for comfortable writing.
As disclosed and discussed in U.S. Pat. No. 6,273,627 assigned to A.T.X. International, Inc., compact devices of all types are sometimes preferred over full-size versions because they occupy less space. However, some compact devices are not as useful as full-sized versions of the same product for a variety of reasons. In the case of writing instruments, a small or reduced size pen can be difficult to hold and use for many people, including the elderly, children, the infirm, and people with large fingers. At the same time, a pen or pencil which occupies less space is more easily carried in a pocket or purse. Sometimes, pens and pencils are sized to fit with other products they are used with, such as a miniature pen provided with a date planner or a golf pencil stored on the steering wheel of a golf cart. These smaller pens and pencils are non-refillable and must be discarded when the ink or lead is used up. While these writing instruments are a compact, convenient size for storing, they are not as comfortably for writing with and suffer the problem that they can be difficult for some persons to use.
If an expandable and retractable writing instrument is desired that also is capable of extending its writing tip for use and retracting it for storage, some further mechanism is needed to permit both actions. U.S. Pat. No. 6,273,627 discloses an expandable pen with the capacity that has a pen body, a front barrel threaded to the pen body and a cap and cap liner that are slidably mounted on the pen body. A cam is rotatably connected inside the pen body at the back end of a refill cartridge for rotation about an axis that is transverse to the main instrument axis. The cam has a rounded surface at one end and a tooth at the other. Pulling the front barrel and the cap in opposite directions causes a ledge in the cap liner to contact the cam tooth and force the cam to rotate downwardly so that the rounded surface of the cam contacts the refill cartridge and forces the refill to move forwardly and past a writing point opening the pen body.
U.S. Pat. No. 7,066,042 assigned to Sanford (Sanford '042) is directed to an advancing/retracting mechanism for a writing instrument which includes a pair of cams and a barrel having a helical surface and a slot. The cams have facing angled surfaces. The first cam has a tab that rides on the helical surface of the barrel and a post. The second cam has a slider which slidably engages the slot of the barrel. In the retracted position, the first cam and second cam are nested. The first cam is moved by applying a force to the post which causes the tab of the first cam to ride on the helical shaped surface. The movement of the tab, in turn, causes the first cam to rotate relative to the barrel and move linearly toward the bottom of the barrel. The first cam moves the second cam until the cams are in an extended position where their tips abut. The second cam transmits the axial motion to an ink refill.
Although the Sanford '042 patent discloses two cams having matching cam edges that are nested together when the writing instrument is closed, this patent does not disclose or suggest a cam geometry nor a helix track of the subject invention. Further, although the Sanford '042 patent discloses a helical surface for a cam follower, there is no teaching or suggestion of a continuous helical loop of the helix cylinder. In addition, as will be explained later in this disclosure, the retracting/expansion mechanism of the subject invention works by pulling the cap away from the pen body which causes a helix cylinder to rotate relative to a shuttle cam for extending the pen. In contrast, with respect to the Sanford '042 patent, a pushing force activates rotation of the first cam for extending the writing instrument. The mechanism of the Sanford '042 patent, moreover, uses a notch in the barrel that engages the slider of the second cam for retaining the writing instrument in an extended position. Releasing the notch, causes the first cam to rotate in a reverse direction and the tab of the first cam to ride on the same helical path until the writing instrument is closed. In contrast, a nub in the cap liner of the subject invention does not travel in reverse on the same path when the pen changes from the extended state to the retracted state. Rather, the nub travels on a left helical track which is missing altogether from the Sanford '042 patent.
U.S. Pat. No. 7,329,063 assigned to Katoh Kinzoku Kougyo Kabushiki Kaisha (Katoh '063) discloses an extendable/contractible writing instrument including a body with a cap at one end that can be attached and detached, a sheath that slides freely on a posterior narrow body section of the body, a slotted rotating shaft on the inside of the body that is fixed to the posterior portion of sheath through top cap, a slotted lead chamber inside rotating shaft which is loaded with an ink refill and an attached casing that is connected to a posterior narrow portion of a lead chamber. By rotating or twisting the body and sheath to extend each from one another, a rotational movement is imparted to the rotating shaft which is converted into the linear movement of the lead chamber and the attached casing, such that the ink refill protrudes from a hole in cap. At the same time and by further rotation and extension of the body and sheath, the attached casing moves in the direction of opening of top end cap and an auxiliary tool such as a silicon gum eraser, that is attached to the tip of casing, protrudes from opening in the top end cap.
U.S. Pat. No. 6,942,411 also assigned to Katoh is directed to a telescopic ball-point pen having an interior surface of a body and a corresponding exterior surface of a sliding axial tube which form a driver screw portion that permits the sliding axial tube to slide back and forth within the body. An interior surface of the sliding axial tube and a corresponding exterior surface of a refill tank form a follower screw portion which permits the refill tank to slide back and forth within the sliding axial tube. A pen refill is received within the refill tank. At a rear end of the sliding axial tube, a sheath and a cap are provided, both of which are configured to rotationally slide along a connection portion of the body. When the sheath and the body are rotated, they are moved away from each other, or closer together, and at the same time, the pen tip of the ball-point pen refill within the refill tank is projected beyond, or received within the writing point.
U.S. Pat. No. 3,679,318 to Liguori discloses a plunger for a writing instrument having a top cam with a wall and an inclined face. A cam follower moves on the cam surface and advances the plunger and the refill cartridge element attached to the plunger when the barrel is rotated.
U.S. Pat. No. 4,533,271 to Sansevero (Sansevero '271) is directed to a writing instrument having two ink refills which uses a tubular cam having two diametrically opposed helical slots whose upper and lower terminations are adjacent. The cam together with cam followers positions one ink refill in the extended position and the second ink refill in the retracted position.
A need remains for a new and improved expandable writing instrument that has a compact closed position for storage and carry, and an extended open position for comfortable writing, and that automatically extends its writing tip from the instrument's front body section, smoothly and effortlessly when the instrument is expanded to its open position.